YACT: Check Engine Codes

[PricklyPete]

My younger sisters car ('98 Mazda Millenia, 2.5L) had the check engine light come on. I took her to Autozone and we had the codes read. They ended up being:

1) P0400: Exhaust Gas Recirculation Flow Malfunction

2) P0325: Knock Sensor 1 Circuit Malfunction (Bank 1 or Single Sensor)

Her car has about 65K miles on it and had a few things replaced recently including her timimg belt and other belts along with a faulty alternator (like 3-4k miles ago).

Anyway, my question is what exactly do these two error codes mean and how severe are they.

I know where the EGR valve is and was thinking that possibly cleaning it would fix the P0400 code. A friend gave me the advice of spraying carb cleaner up inside of it...is this a good idea or will that hurt the valve/recirculation system?

I do not know where the Knock sensor is and my understanding of knock sensors are that they attempt to detect whether any cylinders are firing prematurely and causing the engine to knock. What do they do to compensate for this? Somehow reduce the compression or some other variable in combustion? That might be a stupid question, but I really don't know.

Any help would be greatly appreciated. I'd like to try and fix some of this for her if I can.

Thanks.

 

[StageLeft]

I do not know where the Knock sensor is and my understanding of knock sensors are that they attempt to detect whether any cylinders are firing prematurely and causing the engine to knock. What do they do to compensate for this? Somehow reduce the compression or some other variable in combustion? That might be a stupid question, but I really don't know.

They just pull back the timing. I've not replaced one, but I suspect that they are no harder than replacing an O2 sensor or something similar. If that's the case you need only buy a new one and replace it, then reset the code (with a scanner or disconnecting the battery for a while and letting it sit), then you're good.

In regards to the EGV valve I couldn't say for sure.

I'll ask though did both of these codes come on at the same time? Sometimes codes can be weird. You might have none, and then all of a sudden two or three. But it's not like two or three components really failed at the same time. Sometimes they can be related (ie, fix one and the other one or two are better), and sometimes even the codes will be off. Somebody here recently had a bad o2 sensor reading, but it turned out that when he brought it to nissan they diagnosed it as a bad crankcase sensor instead.

I don't know how often knock sensors really go out, but I'd think about dealing with the EGR valve issue first, then resetting codes, then see what happens instead of both at once.

 

[PricklyPete]

Originally posted by: Skoorb

I do not know where the Knock sensor is and my understanding of knock sensors are that they attempt to detect whether any cylinders are firing prematurely and causing the engine to knock. What do they do to compensate for this? Somehow reduce the compression or some other variable in combustion? That might be a stupid question, but I really don't know.

They just pull back the timing. I've not replaced one, but I suspect that they are no harder than replacing an O2 sensor or something similar. If that's the case you need only buy a new one and replace it, then reset the code (with a scanner or disconnecting the battery for a while and letting it sit), then you're good.

In regards to the EGV valve I couldn't say for sure.

I'll ask though did both of these codes come on at the same time? Sometimes codes can be weird. You might have none, and then all of a sudden two or three. But it's not like two or three components really failed at the same time. Sometimes they can be related (ie, fix one and the other one or two are better), and sometimes even the codes will be off. Somebody here recently had a bad o2 sensor reading, but it turned out that when he brought it to nissan they diagnosed it as a bad crankcase sensor instead.

I don't know how often knock sensors really go out, but I'd think about dealing with the EGR valve issue first, then resetting codes, then see what happens instead of both at once.

That sounds familiar on adjusting the timing...should have thought of that. Anyway, I totally agree that these are probably related and if one is fixed, the other might just go away.

Currently my game plan was to attempt to clean the EGR valve, hook it back up, and then reset the codes and see if they come back on. I was just wondering if ignoring these could cause some major problems in the long run.

Also, I was wondering if I was going to be damaging the EGR valve spraying carb cleaner in there.

At Autozone, the EGR Valve is $221 and the Knock Sensor was $99. I'd love avoiding the replacement of the EGR valve.

 

[StageLeft]

I was going to ask - damn that is pricey for an EGR valve. I know that some people spray carb cleaner into throttle bodies, but I couldn't say on the egr valve. And some think it's a bad idea to spray into TBs anyway. Then others say not to use carb cleaner, but instead a more appropriate chemical. Hopefully somebody here can advise Roger?

 

[PricklyPete]

Yeah...I thought it was pricey too. My sister's face went pretty sour when she heard that. It should be a pretty easy replacement job though...fairly easy to get to in her car.

 

[StageLeft]

You could try ebay

 

[PricklyPete]

Originally posted by: Skoorb
You could try ebay

You never know...

 

[PricklyPete]

bump for some additional help...

 

[huesmann]

All those codes mean is that the voltage (or whatever) on those two sensors went out of range at least one time since the computer was last cleared. Before blowing any cash on this, you should reset the codes so they are gone from the computer's memory. If the CEL comes back on again and you get the same codes, then you can begin to worry.

First things first: the EGR valve error. If this code appeared over the winter, odds are good that it's just a one-time deal. EGR valves/sensors are notoriously cranky during cold weather, commonly giving errors. If you get the code again during warm weather, first try a R&R on the part. When you have it off the car, try cleaning it with some carb cleaner or some such. Often, soot buildup can cause error codes.

I bet the knock sensor code is related to the EGR code.

 

[Quixfire]

P0400 is the code you should address first. This code was set because when the PCM commanded the EGR valve to open or close it did not seen a change in voltage in the EGR Flow sensor. Most likely the valve stuck open causing a lean run condition-creating detonation, cylinders get too hot when lean, setting the knock sensor code. I would look for restrictions in the EGR tube or valve seat that would have cause this condition.

Good Luck,
Quixfire

 

[Vette73]

Did you have them reset the light? That is the first thing I would do. OBD2 is very quick, so even if a sensor is off for juts a second you will get a light. If you reset it and it somes back on then....\

1. Juts because you got a EGR code does not mean the EGR valve is bad. It could be a egr switch, sensor, etc... Aldo you could have a bad wire/line, clogged up egr tube etc...

2. The knock sensor might be acting up as the EGR SYSTEM has a problem, to lean or rich. So worry about the EGR SYSTEM first then see if the knock sensor fixs comes back on.

 

[PricklyPete]

Originally posted by: Marlin1975
Did you have them reset the light? That is the first thing I would do. OBD2 is very quick, so even if a sensor is off for juts a second you will get a light. If you reset it and it somes back on then....\

1. Juts because you got a EGR code does not mean the EGR valve is bad. It could be a egr switch, sensor, etc... Aldo you could have a bad wire/line, clogged up egr tube etc...

2. The knock sensor might be acting up as the EGR SYSTEM has a problem, to lean or rich. So worry about the EGR SYSTEM first then see if the knock sensor fixs comes back on.

My sister told me that she had the CEL on before, but when she had the oil changed last (a couple weeks ago) she mentioned it to the guy and he told her he "fixed" it. I am thinking he just reset it and sent her on her way as he charged her nothing.

I am going to try cleaning/testing the EGR system and then reset the light. Then I'll see if the light comes on anytime in the near future. Thanks for the help guys.